Nanostructuring of materials increases strength and hardness by the effect of blocking of dislocation motion (or dislocation multiplication). For example, the effect takes place when the size of nano-crystal of polycrystalline material is about 10-60 nm for metals. In addition, nanostructuring changes transport and optical properties. This effect is usually used for semiconductors. For example, phonon-blocking/electron-transmitting effect of nanostructured materials is used to increase figure of merit of thermoelectric materials. One of typical synthesis procedures of nanostructured materials is sintering of bulk materials from preliminary synthesized starting nano-blocks. The nano-blocks themselves can be nanocomposite material.
Up to now, improvements of mechanical, transport and optical properties of materials by means of nanostructuring were considered as separate problems. Meanwhile, principally new constructional material, e.g. for external layer for superconductive cables, can be created if properties of nanostructured metal with increased strength and hardness (dislocation blocking effect) will be combined with the possibility of design and modification of transport and optical properties in one universal nano-block. Properties of the starting nano-blocks determine properties of bulk material if the nano-blocks are not destroyed during sintering.
For industrial applications the following requirements are important. The production of the nano-blocks must be effective from technological point of view, especially mass production should be possible. The nano-blocks must be suitable for sintering of bulk materials. The procedure of monitoring and control of the nano-blocks during synthesis must be fast and simple.
By definition, C60 ball-shaped (as well as extended balls C70, C80, or C36, etc.) molecules are called fullerene. In addition to the term “fullerene” the terms “fullerite” and “fulleride” are used. Derivatives of fullerene, e.g. polymerized fullerene molecules bonded by covalent bonds, are called fullerites. Chemical compositions of fullerene/fullerite with other chemical elements, clusters, etc. are called fullerides, e.g. metal fulleride.
Electronic structure modification of fullerenes by metals (metal fulleride) is proposed in U.S. Pat. No. 5,391,323, U.S. Pat. No. 5,196,396 and U.S. Pat. No. 5,698,497. The modification increases electrical conductivity of fullerene-based material. In EP 1 199 281 A1, U.S. Pat. No. 5,294,600, U.S. Pat. No. 5,324,495, U.S. Pat. No. 5,223,479 and U.S. Pat. No. 5,348,936 methods of making metal fulleride were proposed. Base idea of these methods is to produce metal fulleride by an ion exchange reaction in a liquid media. After synthesis, the metal fulleride is Men(Cx)m wherein Cx is a fullerene anion, preferably C60 or C70, and Me is a metal cation. n and m are determined by the valences of fullerene and metal. n typically does not exceed 10 for m=1 (see U.S. Pat. No. 5,348,936).
In U.S. Pat. No. 5,223,479 superconducting, metal-doped fullerenes are provided, along with processes for their preparation in relatively high stoichiometric purity. In one embodiment, the processes provide fullerenes of the formula M3C60 where M is an alkali metal. The processes comprise contacting C60 with alkali metal in an amount and under reaction conditions effective to produce a compound having the formula MyC60, where y is greater than 3, and contacting said MyC60 with a portion of C60 in an amount and under reaction conditions effective to produce said M3C60.
In U.S. Pat. No. 5,348,936 also superconducting, metal-doped fullerenes are provided. In one embodiment, the processes provide fullerenes of the formula MxCq, where M is a metal, x is greater than 0 but less than about 10, and q is at least 60.
In U.S. Pat. No. 5,196,396 a method for making a superconductor fullerene composition is described, which includes reacting a fullerene with an alloy, and particularly reacting C60 with a binary alloy including an alkali metal or a tertiary alloy including two alkali metals in the vapour phase.
In U.S. Pat. No. 5,324,495 a process for making metal fulleride compositions having the formula An(Cx)m, wherein A is a metal cation and Cx is a fullerene anion is provided. Preferably Cx is C60 or C70. n is a number equal to the absolute value of the valence of the fullerene anion. m is equal to the absolute value of the valence A. The values of n and m are divided by their greatest common factor, if any, and the metal fulleride composition is neutral in charge. This process comprises reacting a metal with a fullerene in a solvent or mixture of solvents in which the fullerene is at least partly soluble at a temperature from greater than the freezing point to equal or less than the boiling point of the solvent, for a time sufficient to form the metal fulleride composition.
Effective control, especially by use of Raman scattering, of Me-fullerene interaction have been reported in V. N. Denisov et al. Optics and Spectroscopy, Vol. 76. No. 2, pp. 242-253 (1994). Raman spectra show low-frequency shifts of 5 cm−1 per electron transferred from metal to fullerene at least for bands of 1424, 1468 and 1574 cm−1. Analogous shift has been observed for IR spectra of metal fulleride in P. Rudolf, et al. Report of Brookhaven National Laboratory, contract number DE-AC02-98CH10886, Department of Energy, 2000.
The metal fulleride materials, which are considered above, have restricted technological applications. For example, the metal fulleride, which is described above, is a weak molecular crystal. For creation of material with enhanced mechanical properties, high pressure, preferably above 8 GPa, and high temperature, preferably above 900° C., are required as described in U.S. Pat. No. 6,245,312.
Synthesis of aluminium-fullerene composite fabricated by high pressure torsion has been reported in T. Tokunaga et al. Scripta Materialia 58 (2008) 735-738. The starting material in this publication is mixture of 75 μm powder of aluminium with 5 wt. % of fullerene. The high pressure torsion was performed with a pressure of 2.5 GPa. High pressure torsion is a well-known procedure for nanostructuring of metals. According to the publication, adding fullerene to starting aluminium powder with a graining of 75 μm leads to decreasing crystalline size of aluminium after treatment to 80 nm in comparison with 500 nm without fullerene. No data about bonding aluminium-fullerene or modification of transport properties of aluminium have been reported.
Mechanical alloying of Me and fullerene C60 or C70 in a ball mill has also been reported in M. Umemoto et al. Material Science Forum, Vols 312-314, pp. 93-102 (1999). According to this publication, “molecular structure of C60 (C70) is lost when metal was Cu, Fe, Ni or Sn”. In the case of Al, the remaining fraction of C60 is about 1% of the initial quantity.